diff --git a/sdks/go/pkg/beam/core/runtime/exec/sdf.go b/sdks/go/pkg/beam/core/runtime/exec/sdf.go
index be4f491b04cf..3a1812f06027 100644
--- a/sdks/go/pkg/beam/core/runtime/exec/sdf.go
+++ b/sdks/go/pkg/beam/core/runtime/exec/sdf.go
@@ -190,7 +190,8 @@ func (n *SplitAndSizeRestrictions) StartBundle(ctx context.Context, id string, d
 func (n *SplitAndSizeRestrictions) ProcessElement(ctx context.Context, elm *FullValue, values ...ReStream) error {
 	rest := elm.Elm2.(*FullValue).Elm
 	ws := elm.Elm2.(*FullValue).Elm2
-	mainElm := elm.Elm.(*FullValue)
+
+	mainElm := convertIfNeeded(elm.Elm, &FullValue{})
 
 	splitRests := n.splitInv.Invoke(mainElm, rest)